A temperature-dependent switching mechanism of this type and also a temperature-dependent switch equipped therewith are known for example from DE 43 45 350 A1.
The known temperature-dependent switch comprises a housing with a metal lower part and a metal cover part. A temperature-dependent switching mechanism is accommodated in the housing, and said switching mechanism, depending on the temperature thereof, produces an electrically conductive connection between the lower part and the cover part of the housing.
The switching mechanism is provided with a spring snap-action disc and a bimetal snap-action disc. Here, the spring snap-action disc carries what is known as a movable contact part and serves as contact member, which movable contact part is pressed by the spring disc against a stationary counter contact internally on the cover part, which forms a first contact surface. The spring snap-action disc is supported by means of the rim thereof on a second contact surface in the lower part of the housing, such that the electric current flows from the lower part, through the spring snap-action disc and the movable contact part, into the stationary counter contact and from there into the cover part.
The lower part of the housing is pot-like, and on the inner side thereof has a peripheral shoulder on which the spring snap-action disc of the temperature-dependent switching mechanism rests.
The spring snap-action disc carries centrally a welded contact part, over which the bimetal snap-action disc is put, such that the bimetal snap-action disc rests loosely on the spring snap-action disc.
The cover part of the housing rests on a further peripheral shoulder of the lower part. Because the lower part and cover part of the housing are fabricated from electrically conductive material, an insulating foil is arranged therebetween, which foil electrically insulates the lower part and cover part of the housing with respect to one another.
The outer surface of the cover part of the housing serves as a first outer connection, and a first stranded wire is soldered on there. The outer surface of the lower part serves as a second outer connection, and a connection point is fixed there, to which a second connection stranded wire is soldered.
The known temperature-dependent switch is used to protect electrical devices against overheating. For this purpose, said switch is mounted on the device to be protected, such that the switch is in thermal contact with the device.
The supply circuit of the device is guided via the temperature-dependent switch by connecting a connection cable of the device to one of the outer connections of the switch and by connecting the other outer connection of the switch to the voltage supply for the device.
Due to the thermal coupling, the temperature-dependent switch always has the temperature of the electrical device to be protected. If the temperature of the device now rises above a predefined response temperature, the bimetal snap-action disc thus transfers into the high-temperature position thereof, in which it opens the switch, such that the supply circuit of the device is interrupted, and consequently the device cannot heat up further.
With this construction, the bimetal snap-action disc is arranged in a mechanically force-free manner when below the transition temperature thereof, wherein the bimetal snap-action disc also is not used to conduct the operating current of the device to be protected.
Here, it is advantageous that the bimetal snap-action discs have a long mechanical service life, and that the switching point, that is to say the transition temperature of the bimetal snap-action disc, does not change even after many switching operations.
In addition, it is known to provide switches of this type with a parallel resistor, which is connected in parallel with the external connections. This parallel resistor, when the switch is open, takes on some of the operating current and holds the switch at a temperature above the transition temperature, such that the switch does not automatically close again after cooling. Switches of this type are called self-holding switches.
It is further known for switches of this type to be equipped with a series resistor, through which flows the operating current flowing through the switch. A resistive heat, which is proportional to the square of the flowing operating current, is thus produced in the series resistor. If the amperage exceeds an admissible measure, the heat of the series resistor thus causes the switching mechanism to be opened.
A device to be protected is thus then already switched off from the supply circuit thereof in the case of an excessively high current flow that has not yet even caused the device to be excessively heated.
In contrast to the embodiment of the switch according to DE 43 45 350 A1, the temperature-dependent switching mechanism may also comprise merely a bimetal snap-action disc, which carries the movable contact part and thus conducts the operating current.
When the temperature-dependent switch is to conduct particularly high currents, a current transfer member in the form of a contact bridge or a contact plate is often used as a contact member and is moved by a spring part, that is to say a spring snap-action disc and/or a bimetal snap-action disc, and carries two contact parts, which cooperate with two stationary counter contacts, which are electrically connected to the outer connections of the switch.
The operating current of the device to be protected thus flows from the first counter contact, via the first contact part, into the contact plate, through said contact plate to the second contact part, and from here into the second counter contact. The spring part is thus free of current flow.
It is also known to form a contact bridge on the spring part itself, that is to say for example the bimetal snap-action disc or a spring snap-action disc working against a bimetal part, and said contact bridge therefore is not a separate component. The operating current then flows through the spring snap-action disc thus equipped.
All of these different construction variants can be implemented with the switch according to the invention.
The switching function of the switching mechanism known from DE 43 45 350 A1 can only be tested reliably once the switch has been fully assembled.
This is associated with the immediately evident disadvantage that the entire switch has to be rejected both in the event of problems with the contact making of the movable contact part and/or of the spring snap-action disc and also in the event of a malfunction or incorrect installation of the bimetal snap-action disc.
Although the known temperature-dependent switching mechanism and also the known temperature-dependent switched equipped therewith meet all requirements in terms of function, there is therefore a need to improve the testing capability and assembly.
A further disadvantage with the known switch lies in the fact that at least the lower part of the housing has to be fabricated very precisely so that the spring snap-action disc can be supported reliably via the rim thereof on the peripheral shoulder. On this basis, the lower parts of the known temperature-dependent switch are rotary parts, generally made of brass, which does signify highly precise manufacture, but is associated with high production and unit costs.
Although temperature-dependent switches of this type have proven very effective in everyday use, the assembly of the switch is still time-consuming and cost-intensive, wherein a testing of the known switch is only possible following complete assembly.
DE 195 27 254 A1 discloses a temperature-dependent switch having a housing wherein a temperature-dependent switching mechanism comprised of a bimetal and a spring snap-action disc is arranged. The bimetal and spring snap-action discs are captively held at a movable contact part. The bimetal snap-action disc is arranged with its rim between a shoulder of an annular isolating ring and a housing cover part. Beneath the bimetal snap-action disc the spring snap-action disc is provided and arranged with its rim loosely between a contact ring on an inner bottom of the housing lower part and an electrically conductive distance ring. The relative arrangement of the spring and bimetal snap-action discs with respect to each other can be reversed.
DE 86 90 150 U1 discloses a temperature-dependent switch wherein a rectangular bimetal snap-action disc is arranged below a carrier plate and loosely held in place via protrusions extending over the edges of the bimetal snap-action disc.
DE 20 2005 019 880 U1 discloses a temperature-dependent switch wherein a circular bimetal snap-action disc is arranged below a heat transfer plate and loosely held in place via four hooks extending over the rim of the bimetal snap-action disc.
DE 10 2011 119 633 B1 discloses a temperature-dependent switch having a housing wherein a temperature-dependent switching mechanism comprised of a bimetal and a spring snap-action disc is arranged. The bimetal and spring snap-action discs are captively held at a contact plate cooperating with two stationary contacts provided at an inner side of the housing cover part. The spring snap-action disc is arranged above the bimetal snap-action disc and is guided with its rim between an inner shoulder of the housing lower part and a ring arranged between said shoulder and the cover part.